Zi)b STUDIES IN SYMBIOSIS. 1., 



the fungi normally present. When the fungi are present, the higher plants 

 show signs of "mineral starvation." The cases of known mycorhiza, according 

 to Stahl, occur in such plants which grow in humus or, for other reasons, show 

 feeble intake of mineral substances. He also asserts that the fungus not only 

 absorbs but transforms the mineral salts for the higher symbiont. He comes to 

 this conclusion from the observation that most mycotrophic plants do not eon- 

 tain calcium oxalate, which is associated with the assimilation of nutritive 

 salts. In regard to the absence of calcium oxalate, I can definitely state that in 

 Dipodiwm, which possesses an endophytic mycorhiza communicating with the 

 hyphae outside the plant, there are large numbers of raphide-crystals in the 

 cells of the cortex. 



The Plant. 



Dipodium pwnctatum is a terrestrial orchid which has very small scale- 

 leaves. From a few large fleshy, succulent roots which penetrate the substratum 

 in various directions, there develops the single upright flowering axis. The 

 most favourable habitat of this orchid is the shaded humus soil of the Aus- 

 tralian Bush, where there is a considerable accumulation of decaying leaves 

 among-st a rich black sand. It occurs in a more stunted form on clay soils. 

 Various species of Eucalyptus, and Angophora lamceolata provide a certain 

 amount of shade when gTowing fairly closely together. 



Moore and Betche (Flora of New South Wales) record Dipodium pwnctatum 

 as a parasite on roots of neighbouring plants, but, although I have made most 

 careful investigation of the root system in the soil, and have excavated it in its 

 entirety I have not found any evidence to warrant the statement that it is a 

 parasite on roots. I found no connection with the roots of other plants, and 

 the statement that this orchid is a parasite has probably been made on account 

 of the practically leafless, chlorophyll-less, aerial, flowering shoot. 



Beccari (1871) has described a Monocotyledon, Pf.trosavia stellaris, as a 

 . parasite on roots, but Groom (1895a) has described a plant which he pro- 

 visionally named Protolirion paradoxum which is very like the Petrosavia of 

 Beccari. Groom found that his plant, Protolirion, was a saprophyte, and sus- 

 pects that Petrosavia of Beccari is also a saprophyte, The existence of Phanero- 

 gamic holosaprophytes was not recognised at the time and it was assumed that 

 non-ehlorophylliferous forms were parasitic. 



It is highly probable that the assertion that Dipodium punetatum is a 

 parasite upon roots was based upon this assumption, and the non-recognition of 

 holosaprophytism amongst Angiosperms. All the Monocotyledons devoid of 

 chlorophyll, represented by all the Triuridaceae, etc., nearly all the Burman- 

 niaceae, and several Orehidaoeae are saprophytic. The probability is, therefore, 

 from theoretical grounds, that Dipodium pwnctatum is saprophytic. From in- 

 vestigation I can confirm this view. 



The flowering stems are from one to two feet high, and of a reddish colour, 

 the leaves are small and scale-like, almost membranaceous. The flowere arise in 

 the axils of the scale-leaves forming an extended terminal raceme. The plant 

 is devoid of chlorophyll, and the leaves have no power of photosynthesis. They 

 probably protect the young flower-buds. 



Structure of the root. — The root is covered superficially by a distinctive 

 zone, of three or four layers, of colourless thin-walled cells elongated radially. 

 There are no root hairs. The cells contain very little protoplasm, which is 

 confined to the periphery of the cells; they fit together closely, leaving only the 



